1. Field of the Invention
The invention relates to an impact damper for a vehicle having two tubes which are slidable one in the other. The impact damper brakes a vehicle impacting against an obstacle by hydraulic damping forces and pneumatic spring forces. The impact damper includes an inner tube closed off by a bottom, a gas chamber adjacent to the bottom of the inner tube and containing a high-pressure gas cushion, a separating piston guided sealingly and displaceably in the inner tube, a first fluid chamber in the inner tube separated from the gas chamber by the separating piston, a partition fixed in the inner tube and provided with choke openings, and a second fluid chamber formed by an outer tube and connected to the first fluid chamber via the partition.
2. Description of the Related Art
A prior art hydropneumatic impact damper for a vehicle is known from DE 24 04 706, in which an inner tube is pushed into an outer tube in the event of a collision. The inner tube has a gas chamber which contains a gas cushion and is separated in a sealed manner in relation to a first fluid chamber by a separating piston. The first fluid chamber is in turn delimited at the end of the inner tube by a partition which has a choke bore so that such that fluid in the first fluid chamber in the inner tube can flow toward a second fluid chamber which is formed by the outer tube therethrough.
The impact damper has connection elements on the inner tube and on the outer tube for the vehicle body and a vehicle fender.
In the event of a collision, the inner tube moves into the outer tube and displaces damping fluid out of the second fluid chamber through the choke opening of the partition into the first fluid chamber of the inner tube, a damping force being generated. The increasing volume of the first fluid chamber is compensated by the separating piston being displaced. Purely hydraulic damping takes place, which, however, is suitable only up to an impact range of 4-8 km/h. Above this energy absorption threshold, the fender and/or the body parts adjacent to the impact damper will be permanently deformed.
Another prior art impact damper is known from DE 34 19 165 which has, in addition to hydraulic damping, a deformation damper in the form of a folding tube. As soon as the energy absorption threshold for the hydraulic damping is exceeded, deformation of the deformation tube occurs up to an energy absorption threshold of roughly 15 km/h. This involves a serious disadvantage because, after a collision, a permanent change in length of the impact damper must be accepted. Moreover, an impact damper of this type of construction has the disadvantage that all the construction spaces, that is to say the first fluid chamber, second fluid chamber and the gas chamber, are arranged in a row, to which the construction space for the deformation tube is in turn adjacent.
Precisely the same disadvantages are present in another prior art impact damper known from EP-A 0.473.955. In this prior art device, a deformation piston is displaced inside a deformation tube, the deformation piston being connected to the hydraulic damping arrangement via a piston rod. In addition to the above-mentioned disadvantages, the piston rod between the hydraulic damping arrangement and the deformation piston involves the disadvantage that the piston rod has elastic properties so that the damping force as a function of the travel has a maximum which can be defined only with difficulty so that the risk is not excluded that the vehicle body will deform before the deformation body on the impact damper comes into play.
An impact damper with a deformation body is also known from DE 44 03 127 A1, in which a partition fixed in the inner tube is provided. Above a given energy absorption threshold, the partition is displaced toward the gas chamber from its original mounting position, with deformation of the inner tube.